Terpenes elucidation

Terpenes are characterized as being made up of units of isoprene in a head-to-tail orientation. This isoprene concept, invented to aid in the stmcture deterrnination of terpenes found in natural products, was especially useful for elucidation of stmctures of more complex sesquiterpenes, diterpenes, and polyterpenes. The hydrocarbon, myrcene, and the terpene alcohol, a-terpineol, can be considered as being made up of two isoprene units in such a head-to-tail orientation (1). 

After identification of A9-THC as the major active compound in Cannabis and its structural elucidation by Mechoulam and Gaoni in 1964 [66], a lot of work was invested in chemical synthesis of this substance. Analogous to the biosynthesis of cannabinoids, the central step in most of the A9-THC syntheses routes is the reaction of a terpene with a resorcin derivate (e.g., olivetol). Many different compounds were employed as terpenoid compounds, for example citral [67], verbenol [68], or chrysanthenol [69]. The employment of optically pure precursors is inevitable to get the desired (-)-trans-A9-THC. 

The possible occurrence of such major rearrangement of a compound s carbon skeleton, during the course of apparently unequivocal reactions, is clearly of the utmost significance in interpreting the results of experiments aimed at structure elucidation particularly when the actual product is isomeric with the expected one. Some rearrangements of this type are highly complex, e.g. in the field of natural products such as terpenes, and have often made the unambiguous elucidation of reaction pathways extremely difficult. The structure of reaction products should never be assumed but always confirmed as a routine measure lH and 13C n.m.r. spectroscopy have proved of enormous value in this respect. 

Although the mesoporous materials, such as Ti-MCM-41, have lower intrinsic epoxidation selectivity than TS-1 and Ti-beta, they must nevertheless be used as catalysts for reactions of large molecules typical in the fine chemicals industry. It is, therefore, interesting to elucidate how these ordered mesoporous materials compare with the earlier generation of amorphous titania-silica catalysts. Guidotti et al (189) recently compared Ti-MCM-41 with a series of amorphous titania-silica catalysts for the epoxidation of six terpene molecules of interest in the perfumery industry (Scheme 6). Anhydrous TBHP was used as the oxidant because the catalytic materials are unstable in water. The physical characteristics of these catalysts are compared in Table XII. 

Terpene structures and their elucidation. Perfum. essential Oil Rec. 43,... 

Elucidating the Metabolism of Plant Terpene Volatiles Alternative Tools for Engineering Plant Defenses ... 

Agelasidines A-D (275-279) are a series of terpene derivatives of hypotaurocyamine and were isolated from sponges of the genus Agelas. Agelasidine B (276) and (+)-C (277) were obtained from the Okinawan A. nakamurai [201] while agelasidines (-)-C (278) and D (279) were isolated from the Caribbean A. clathrodes [202]. The structures of these compounds were elucidated by interpretation of spectral data and by... 

This reaction is used to determine the presence and position of double bonds in organic compounds it has been much applied to the elucidation of the structure of members of the terpene series. 

In contrast to the polycyclic indole, isoquinoline, or terpene alkaloids, the di- and polyamine alkaloids seem to be of much simpler construction. This first impression is misleading. Special structural features render this group of alkaloids even more difficult to handle than the above-mentioned ones. It should be noted that the structures of several polyamine alkaloids have had to be revised. Because of this, two main factors should be mentioned. (1) The alkaloids sometimes occur as mixtures that are very difficult to separate, and (2) the results from spectral or chemical analyses are equivocal (cf. references on structural elucidation in Section V). This group of alkaloids was the subject of several review papers (26-28) and especially covering the subject of synthesis (29-32). Some general aspects of the difficulties associated with the isolation and structure elucidation of the polyamine alkaloids are discussed. 

Radical cations of three terpenes, sabinene 47, a-thujene 48, and j6-thujene 49, containing vinylcyclopropane functions held rigidly in either an anti- or syn-orientation, are elucidated by CIDNP results observed during there electron transfer reactions with photoexcited (triplet) chloranil [131]. 

Palladium, Pd, and platinum, Pt, usually on activated carbon or asbestos, are catalysts for the dehydrogenation of hydroaromatic and some heterocyclic compounds to aromatic compounds. The reaction takes place at high temperatures (300-350 °C), and consequently, side reactions such as rearrangements often take place [495, 496, 497, 945, 946, 947, 948], The catalytic dehydrogenations played a very important role in the elucidation of terpene and alkaloid structures. Because spectroscopic methods, especially NMR spectroscopy, can help to determine structures much more reliably, catalytic dehydrogenation over palladium and platinum are rare nowadays. 

The Barton reaction was utilized during the synthesis of various terpenes and has played a crucial role in the elucidation of terpene structures. The Barton nitrite ester reaction was a key step in E.J. Corey s synthesis of azadiradione and perhydrohistrionicotoxin . Even though the yields were low, other ways to access the same intermediates would have been tedious, and afforded lower overall yields than in the applied Barton reactions. 

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